T lymphocytes have been implicated as a major cause of pancreatic islet destruction in IDDM as well as animal models of the disease. We hypothesize that the T lymphocytes involved in both diabetes and allograft rejection are tissue specific in nature recognizing islet specific peptides in the context of MHC class I molecules. We will test whether PBL from IDDM patients shown to be islet cell reactive by in vitro screening will recognize the immunogenic islet peptides shown to be reactive with clines isolated from allografted hu-SCID mice. Reactivity with these HLA restricted islet peptides will suggest that certain peptides are immunodominant in both rejection and automimmuity.